<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta http-equiv="X-UA-Compatible" content="IE=edge" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Document</title>
  </head>
  <body>
    <script>
      //将div#demo.demo转化成<div id="demo" class="demo"></div>
      var str = "div#demo.demo";
      var reg = /^(\w+)#(\w+)\.(\w+)$/;
      var str1 = str.replace(reg, function (match, $1, $2, $3) {
        return "<" + $1 + ' id="' + $2 + '" class="' + $3 + '"></' + $1 + ">";
      });
      console.log(str1);
    </script>
  </body>
</html>
